Inhibitors for aqueous phase, radiation polymerization

ABSTRACT

In the polymerization, in which an aqueous phase is employed, of ethylene, or ethylene and other unsubstituted or substituted olefinic monomers by means of an ionizing radiation, formation of an undesirable polymer in the aqueous phase of the reaction system is inhibited by using specific polymerization inhibitors. The inhibitors which have no adverse effect on the polymerization in the non-aqueous phase, comprise the electrolytes which have strong oxidizing action and/or react at high reaction rate with active species such as H radicals, OH radicals and/or hydrated electrons formed by ionizing radiation. According to the present invention, adhesion of undesirable polymer to the reactor walls during polymerization reaction is prevented and contamination which lowers the quality of the main polymer is eliminated.

Unite States Patent 091 Takehisa et a1.

[54] INHIBITORS FOR AQUEOUS PHASE,

RADIATION POLYMERIZATION [75] Inventors: Masaaki Takehisa; Shiro Senrui,

both of Takasaki-shi, Japan [73] Assignee: Japan Atomic Energy Research Institute, Minato-ku, Tokyo, Japan [22] Filed: May 12, 1970 [21] Appl. No.: 36,682

[56] References Cited v UNITED STATES PATENTS 10/1962 Yanko etal. ..204/l59.22 11/1961 Urchick ..204/l59.l5

OTHER PUBLICATIONS Bovey et al., Emulsion Polymerization, Interscience Pub., 1955, PP. 233-236 51 Jan. 30, 1973 Primary Examiner-Murray Tillman Assistant Examiner-Richard B. Turer Attorney-Stevens, Davis, Miller & Mosher [57] ABSTRACT In the polymerization, in which an aqueous phase is employed, of ethylene, or ethylene and other unsubstituted or substituted olefinic monomers by means of an ionizing radiation, formation of an undesirable polymer in the aqueous phase of the reaction system is inhibited by using specific polymerization inhibitors. The inhibitors which have no adverse effect on the polymerization in the non-aqueous phase, comprise the electrolytes which have strong oxidizing action and/or react at high reaction rate with active species such as H radicals, OH radicals and/or hydrated electrons formed by ionizing radiation. According to the present invention, adhesion of undesirable polymer to the reactor walls during polymerization reaction is prevented and contamination which lowers the quality of the main polymer is eliminated.

7 Claims, N0 Drawings INHIBITORS FOR AQUEOUS PHASE, RADIATION POLYMERIZATION BACKGROUND OF THE INVENTION is removed. However, undesirable polymer is formed in the water or aqueous solution phase, when a gas-liquid or liquid-liquid mixed phase system in which the polymerizable monomer phase consists of ethylene, ethylene and another olefinic monomer, or a mixture of said monomer and its organic solvent or diluent and coexists with 'water or aqueous solution phase, is irradiated by an ionizing radiation. In such a mixed phase polymerization system, the inhibition of polymerization in the medium phase such as water or aqueous solution phase is very useful for inhibiting formation of the undesirable polymer derived from the monomer dissolved in the aqueous phase and adhesion thereof to the reactor walls, and further avoiding the lowering of quality of the main polymerwhich would result by being mixed with said undesirable polymer.

Some chemicals which inhibit polymerization.'reac tion have been known; for example, diphenylpicrylhydrazil (D.P.P.H.) is a stable radical per' se, and benzoquinone and' nitrobenzene etc. are chemicals which form stabilized radicals by reacting with propagating radicals. However, such polymerization inhibitors do not selectively'inhibit polymerization in the aqueous phase, and adversely inhibit the desired polymerization reaction in the nonaqueous monomer phase or the overall reactions in the polymerization system, since these inhibitors are non-ionic organic compounds.

SUMMARY OF THE INVENTION The present invention relates to a novel polymerization process for polymerizing ethylene or a mixture of ethylene and other unsubstituted or. a substituted olefinic monomer or monomers. Particularly, it relates to an improvement in polymerization process which comprises using polymerization inhibitors which inhibit or control specifically the polymerization in water or aqueous solution phase and have no adverse effect on the polymerization in the monomer phase, when the polymerization reaction by means of an ionizing radiation is carried out in the gas-liquid or liquid-liquid mixed phase system comprising water or an aqueous solution phase and a polymerizable component phase consisting of ethylene, or mixture of ethylene and other polymerizable monomer or monomers, or mixture of said monomer and its solvent or diluent. The term an aqueous solution phase" means a solution phase comprising water and an organic medium such as a lower alkanol which has been employed in the conventional polymerization processes.

The inventors studied a series of inorganic and-ionic organic compounds which are selectively distributed in the aqueous phase in the mixed phase polymerization reaction of ethylene or ethylene and other olefinic monomers by means of an ionizing radiation, and found that formation of undesirable polymer in aqueous phase is entirely eliminated or remarkably decreased by dissolving one or more chemicals selected from the inhibitors as defined below in the water or aqueous solution phase. Thus, the present invention was completed.

The inhibitors employed in the present invention are (A) the electrolytes which have strong oxidizing action and release nascent oxygen in an ordinary chemical reaction condition, or (B) those which react at a high reaction rate with active species such as H radicals, OH radicals and/or hydrated electrons etc. that formed in the aqueous phase by means of an ionizing radiation and are transformed into stable chemical species by reacting therewith. An inhibitor of (A) group may have the properties of the inhibitor of (B) group and vice versa, however, the following exemplified compounds are classified according to their main properties. The inhibitors (A) typically include bichromates, permanganates and persulfates; inhibitors (B) include nitrates, nitrites, ferric-cyanates, ferro-cyanates, ferric salts, stannic salts, thiosulfates, dithionates, alkalihalides, carbonates as well as phosphonic acid, sulfuric acid, lower organic carboxylic acids and salts of these acids.

By adding a small amount of one or more chemicals selected from the above inhibitors to water or aqueous solution phase prior to the polymerization reaction, the inventors succeeded in eliminating or remarkably decreasing the formation of undesirable polymer in said aqueous solution, in preventing adhesion of said undesirable polymer to the reactor walls, and in preventing the lowering of quality of the main desired polymer which ordinarily results when the polymer mixes with said undesirable polymer. The amount of the inhibitor to be added need not be controlled strictly, but in general, preferably ranges from 10 to 10" mol per liter of water or aqueous solution. it is not desirable to add a large excess of the inhibitor since this necessitates a recovery operation, increases the cost of the operation, and might lower the purity of the product. As shown in Example l, addition of the inhibitor in excess has little effect on the amount of the polymer formed in the aqueous phase.

The inhibitor can be added to the aqueous phase at any stage of the operation before initiating polymerization reaction, by dissolving it in water or aqueous solution phase. The radiation employed in the present in vention is an ionizing radiation known to the art such as gamma rays, X-rays, beta rays, electron beams, neutron beams, alpha rays and mixture thereof etc.

In the present invention, the term an olefinic monomer" means a polymerizable olefinic monomer such as an olefin other than ethylene, a vinyl compound and the other substituted monomers of an olefin. Such a polymerizable monomer can advantageously be employed in the present invention. The olefinic monomers used include propylene, l-butene, vinyl chloride, vinyl acetate, styrene, acrylonitrile, alkyl acrylate, alkyl methacrylate, and vinylidenechloride etc.

v DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is further explained by way of Examples, but is not limited to them. It should be understood that modifications and changes can be effected within the spirit and scope of the present invention.

EXAMPLE l about 70 ml solution comprising; 3ml of cone. H PO and water to make I ml.

EXAMPLE 3 About 70 ml of aqueous solution of sodium nitrite, E l l d h h air dissolved in which was replaced with ethylene con- Xamp f at t e concemfa' mining oxygen not more than 0.4 ppm, was charged in non of sodium nitrite was 1.0 X mol, and the mixa reaction vessel having an inside volume of 100ml. 10 F; of ethylene m0] P 'i and Solvent 2' Then the same species of ethylene was charged into dlc ff was charged p 400 atmospheric pressure at 20 C. The reaction atmospherlc presure at 20 NO P y f f in system was irradiated by gamma rays from of the aqueous solution phase. Under the same conditions absorption dose rate of 0.88 X 10 rad/hr for one hour. when "9 Sodium mime wasfiddedt 8 f Polymer Table 1 shows amounts of polyethylenes formed in formed the aqueous solutionaqueous solut ons in which sodium nitrites are dis- EXAMPLE 4 solved in various concentrations. The formation of polyethylene was ziro W26 ghe clooncentrlzltltiqgi (if sotll1i- Eitzttmple iglas 3repeated elxcepg tlhattlth; Lnhibitgr: um nitrite was not ess t an X mo n er t e speci 16 in a 6 were cmp Oye a e s ows a same conditions except that no sodium nitrite was dis- 20 formation of polyethylene was remarkably decreased. solved, 0.65 g/l of polyethylene formed in the aqueous solution. TABLE 3 TABLEl Formation of Pol eth lenea ainstlnhibitors y y 8 Formation of Polyethylene aga nst Concentration of Yield of Yield of S i N 'l concentration polyethylene polyethylene of inhibitor in aqueous in gaseous Sodium Nitrite concentra- Polyethylene formed in Inhibitor (mol/I) solution phase (gll) tion (mol/l) aqueous solution (gll) /l) 0 0.65 No inhibitor (control) 0.66, 6.0 l X l0" 0.60 NaCl 2 X l0" 0.22 5.5 5 x 10- 0.08 KBr 0.16. 5.7 6 x l0 0.00 Kl 0.20 5.0 i x i0- 0.00 znci 0.29.. 4.2 2 x 10- 0.00 NHCI 0.28, 4.9 K.Fe cN .3ii,0 0.30. 5.5 1,121,58 0.29 4.0 n 0.27 7.0 EXAMPLE 2 ii,so.' solution of cone. 0.18; 6.6 About 70 ml each of aqueous solution of the inhibiiiifigh iiil tor specified in Table 2, air dissolved in which was 40 HCOOH solution ofthe almostzew replaced with ethylene containing oxygen not more 2323 than 0.4 ppm, was charged into a reaction vessel having CH COOH almost zero 3.5 an inside volume of 100 ml. The reaction vessel was charged with the same species of ethylene of 400 atmospheric pressure at 20 C. and was irradiated by 45 EXAMPLES gamma y from f of absorpilon dose rate of L8 lnto a reaction vessel of 100 ml inside volume was X 10 rad/hr for 30 minutes. Formation of polyethylene charged 10 ml f methyl methacryme ifi d by was Zero the aqueous Phase as shown m Table removing polymerization inhibitor) and replaced air dissolved with ethylene containing oxygen not more TABLE 2 than 1 ppm by repeating compression (to 20 atmospheric pressure of ethylene) and decompression. Formation of Polyethylene against Inhibitors About 60 ml of aqueous solution of sodium nitrites (1.0 M X 10' mol/l) was introduced into the vessel after concentration 0| g f is o! if replacing air dissolved in the solution with said of inhibitor p in aqiieous P iii ga eous ethylene. Then the same species of ethylene was ("ml/l) zgy Phase charged to 400 atmospheric pressure at 20 C., and the system was irradiated with gamma rays from Coof absorption dose rate of 0.88 X 10 rad/hr for one hour. no inhibitor control 0.667 6.0 (20,101 2 X Om 60 No polymer formed in the aqueous solution phase. (NH;),S,O,. almost zero 5.0 Under the same conditions, when no sodium nitrite was 6 8%8 2% added, 0.50 g/l of polymer formed in the aqueous solu- NaNO, 0. 0 4. g wmo 8-88 What is claimed is: i b it 1. In a process for effecting polymerization by means N=ii,s,0 0.00 4.8 of an ionizing radiation in the mixed phase system com- 'hfgd 2 X 92 we is prising polymerizable monomer phase consisting of FeCl, 2 x l0" 0.00 5.5 ethylene, mixture of ethylene and another unsubstituted or substituted olefinic monomer or monomers, or a mixture of said polymerizable monomer or monomers and solvent therefor, and water or aqueous solution phase coexisting with said monomer phase; an improvement in inhibiting or decreasing formation of polymer in the aqueous phase, comprising adding a small amount of at least one inhibitor selected from the group consisting of (A) the electrolytes which have strong oxidizing action and release nascent oxygen in an ordinary chemical reaction condition selected from the group consisting of bichromates, permanganates and persulfates, and (B) the electrolytes which react at a high reaction rate with the active species such as H radicals, Ol-l radicals and/or hydrated electrons that form in the aqueous phase by means of anionizing radiation and are transformed into stable chemical species by reaction therewith selected from the group consisting of nitrates, nitrites, ferric-cyanates, ferrocyanates, ferric salts, stannic salts, thiosulfates, dithionates, alkalihalides, carbonates, phosphonic acid, sulfuric acid, lower organic carboxylic acids and salts of these acids, to said water or aqueous solution phase before initiating polymerization wherein said inhibitor or inhibitors is present in an amount of about -10 mol per liter of water or aqueous solution.

5. A process as set forth in claim 1, in which the olefinic monomer is selected from an olefin other than ethylene, a vinyl compound monomer and the other substituted monomers of an olefin.

6. A process as set forth in claim 1, in which the olefmic monomer is selected from the group consisting of propylene, l-butene, vinyl chloride, vinyl acetate, styrene, acrylonitrile, alkyl acrylate, alkyl methacrylate and vinylidene chloride.

7. The process of claim 1 wherein gamma-rays, X- rays, beta-rays, electron beams, neutron beams, alpharays, or mixtures thereof are employed. 

1. In a process for effecting polymerization by means of an ionizing radiation in the mixed phase system comprising polymerizable monomer phase consisting of ethylene, mixture of ethylene and another unsubstituted or substituted olefinic monomer or monomers, or a mixture of said polymerizable monomer or monomers and solvent therefor, and water or aqueous solution phase coexisting with said monomer phase; an improvement in inhibiting or decreasing formation of polymer in the aqueous phase, comprising adding a small amount of at least one inhibitor selected from the group consisting of (A) the electrolytes which have strong oxidizing action and release nascent oxygen in an ordinary chemical reaction condition selected from the group consisting of bichromates, permanganates and persulfates, and (B) the electrolytes which react at a high reaction rate with the active species such as H radicals, OH radicals and/or hydrated electrons that form in the aqueous phase by means of an ionizing radiation and are transformed into stable chemical species by reaction therewith selected from the group consisting of nitrates, nitrites, ferric-cyanates, ferro-cyanates, ferric salts, stannic salts, thiosulfates, dithionates, alkalihalides, carbonates, phosphonic acid, sulfuric acid, lower organic carboxylic acids and salts of these acids, to said water or aqueous solution phase before initiating polymerization wherein said inhibitor or inhibitors is present in an amount of about 10 4-101 mol per liter of water or aqueous solution.
 2. A process as set forth in claim 1, in which the olefinic monomer is selected from an olefin other than ethylene, a vinyl compound monomer and the other substituted monomers of an olefin.
 3. A process as set forth in claim 1, in which the olefinic monomer is selected from the group consisting of propylene, 1-butene, vinyl chloride, vinyl acetate, styrene, acrylonitrile, alkyl acrylate, alkyl methacrylate, and vinylidene chloride.
 4. A process as set forth in claim 1, in which gamma rays, X rays, beta rays, electron beams, neutron beams, alpha rays or mixture thereof is employed.
 5. A process as set forth in claim 1, in which the olefinic monomer is selected from an olefin other than ethylene, a vinyl compound monomer and the other substituted monomers of an olefin.
 6. A process as set forth in claim 1, in which the olefinic monomer is selected from the group consisting of propylene, 1-butene, vinyl chloride, vinyl acetate, styrene, acrylonitrile, alkyl acrylate, alkyl methacrylate and vinylidene chloride. 